Method of fabricating integrally bladed rotor using surface positioning in relation to surface priority

ABSTRACT

A method of fabricating an integrally bladed rotor for gas turbine engines according to one aspect includes a step of positioning a blade on a hub in a joining procedure by using a priority surface of the blade as a reference surface. The priority surface is determined in relation to importance of surface functionality of the blades during engine operation.

CROSS REFERENCED TO RELATED APPLICATION

The present application is a divisional application of U.S. patent application Ser. No. 13/188,535 filed on Jul. 22, 2011, the entire content of which is herein incorporated by reference.

TECHNICAL FIELD

The described subject matter relates generally to gas turbine engines and more particularly, to an improved method of fabricating integrally bladed rotors of a gas turbine engine.

BACKGROUND OF THE ART

Integrally bladed rotors (IBR's), also commonly known as “bladed discs”, are important parts of gas turbine engines. An IBR generally has a disc or hub with an array of blades affixed thereto. The blades extend radially outwardly and are circumferentially spaced apart. The airfoil surfaces of each blade define a complex geometry in order to provide desired aerodynamics. IBR's are used in gas turbine engines, for example as fan rotors which may also be referred to as “IFR's”, compressor rotors or turbine rotors which rotate at high speeds during engine operation either to provide high speed and high pressure gas air flow or to generate power. The accuracy of the complex geometry of the airfoil surfaces of IBR's is important to ensure engine performance. However, it is challenging to achieve the accuracy of the complex geometry of the airfoils of IBR's, due to manufacturing tolerances. For example, when the blades are joined to the hub in a welding process, a reference surface of a blade which is used to define the position of the blade on the hub, can vary up to the addition of positioning tolerance and other manufacturing tolerances of the blade, resulting in deviation of finished surfaces of the blade from the required geometry defined by designed nominal surfaces of the blade. This will affect the performance of the rotors and thus the engine.

Accordingly, there is a need to provide an improved method of fabricating IBR's to minimize IBR geometry variations.

SUMMARY

In accordance with one aspect, the described subject matter provides a method of fabricating an integrally bladed rotor of a gas turbine engine, the integrally bladed rotor including a hub with an array of airfoil blades welded to the hub, the method comprising a) selecting a finished surface of the respective blades as a reference surface for positioning the respective blades in a welding process; b) positioning the respective blades onto the hub such that a position of the selected reference surface of the respective blades on the hub is defined in accordance with design data of a corresponding nominal surface of the integrally bladed rotor; and c) welding the respectively positioned blades to the hub.

In accordance with another aspect, the described subject matter provides a method of fabricating an integrally bladed rotor of a gas turbine engine, the integrally bladed rotor including a hub with an array of airfoil blades welded to the hub, the method comprising a) determining a priority surface of the respective blades in relation to importance of surface functionality of the blades during engine operation; b) positioning the respective blades onto the hub by using the determined priority surface of the blades as a reference surface in order to locate a position of the respective blades on the hub; and c) welding the respectively positioned blades to the hub.

Further details of these and other aspects of the described subject matter will be apparent from the detailed description and drawings included below.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying drawings depicting aspects of the described subject matter, in which:

FIG. 1 is a schematic cross-sectional view of a turbofan gas turbine engine illustrating an exemplary application of the described subject matter;

FIG. 2 is a partial perspective view of an IBR in fabrication showing a second blade being positioned on a hub of an IBR to be welded thereto;

FIG. 3 is a schematic illustration of an IBR during fabrication, showing a blade being positioned on a hub of the IBR according to one embodiment; and

FIG. 4 is a cross-sectional view of a blade taken along line 4-4 in FIG. 2, showing in exaggerated dimensions, variations between designed nominal surfaces and actual finished surfaces of the airfoil blade resulting from manufacturing tolerances.

It should be noted that throughout the appended drawings, like features are identified by like reference numerals.

DETAILED DESCRIPTION

Referring to FIG. 1, a turbofan gas turbine engine which is an exemplary application of the described subject matter includes a fan case 10, a core case 13, a low pressure spool assembly (not indicated) which includes a fan assembly 14, a low pressure compressor assembly 16 and a low pressure turbine assembly 18 connected by a shaft 12, and a high pressure spool assembly (not indicated) which includes a high pressure compressor assembly 22 and a high pressure turbine assembly 24 connected by a turbine shaft 20. The core case 13 surrounds the low and high pressure spool assemblies to define a main fluid path (not indicated) therethrough. The high and low pressure spool assemblies co-axially define a rotating axis 30 of the engine. A combustor 26 generates combustion gases in the main fluid path to power the high and low pressure turbine assemblies 24, 18 in rotation about the rotating axis 30. A mid turbine frame 28 is disposed between the high pressure turbine assembly 24 and the low pressure turbine assembly 18.

Referring to FIGS. 1, 2 and 4, an integrally bladed rotor 32 is fabricated according to one embodiment for use as a rotor in any one of the fan assembly 14, low pressure compressor assembly 16, high pressure compressor assembly 22, low pressure turbine assembly 18 and the high pressure turbine assembly 24 of the engine. The integrally bladed rotor 32 includes a hub 34 which is partially shown in FIG. 2 with an array of blades 36 affixed to the periphery of the hub 34 (only one blade shown being affixed to the hub). The blades 36 stand radially outwardly from the hub 34 and are circumferentially spaced apart one from another. The integrally bladed rotor 32 has a central hole which is partially shown in broken lines 38, axially extending through the hub 34 for receiving the shaft 12 or 20 therein when the integrally bladed rotor 32 is installed in the engine. A geometric center 30 a of the central hole 38 in the hub 34 superposes the rotating axis 30 of the engine within acceptable tolerances when the integrally bladed rotor 32 is installed in the engine. Therefore, the center point 30 a of the central hole 38 of the integrally bladed rotor 32, is used as a reference point representing the rotating axis 30 of the engine in the integrally bladed rotor 32 design and fabrication.

The hub 34 and the individual blades 36, according to one embodiment, are individually fabricated and the individual blades 36 are then welded to the periphery of the hub 34 in a designed blade array pattern. The individual blades 36 are designed, for example in a computer aided design (CAD) program which generates a drawing of the blade with a stacking line 40 at a designated position which determines all positions of the functional surfaces of the blade in the engine. The individual blades are supposed to be accurately identical. However, due to fabrication tolerances, the actually finished surfaces such as finished suction side surface 42 a, pressure side surface 44 a, leading edge surface 46 a and trailing edge surface 48 a, may vary from the corresponding ideal nominal surfaces 42, 44, 46 and 48 of the individual blades 36.

In a conventional welding process such as a linear friction welding (LFW) process in which the individual blades 36 are welded to the hub 34, one of the nominal surfaces (not numbered) of each blade 36 is selected as a reference surface of that blade 36 for positioning the blade with respect to the hub 34 according to design data presented in the drawings (not shown). However, as shown in FIG. 4, the actual finished surfaces of each blade 34 may differ from the corresponding nominal surfaces due to fabrication tolerances in addition to positioning tolerances of each blade 36 in the LFW operation. Therefore, when the blades 36 are joined to the hub 34, the variation in position/orientation of the actual finished surface of the selected reference surface of each blade 36, can deviate up to the accumulation of the various tolerances in blade fabrication and positioning in the LFW operation. In order to minimize this deviation, the actual finished surface rather than the nominal surface of each blade 36 according to one embodiment, is used as the selected reference surface of the respective blade 36 in order to define the position of the reference surface of the blade 36 in relation to the design data of the blade design drawing, for positioning the blade 36 with respect to the hub 34 in the LFW operation. Therefore, stack up tolerances in blade positioning will be reduced to a minimum.

According to another aspect, a priority surface of the respective blades 36 is determined in relation to importance of surface functionality of the blades 36 in engine operation and the determined priority surface of the respective blades 36 may be used as a reference surface to locate a position of the respective blades 36 on the hub 34 in the LFW procedure.

When a finished surface, for example the suction side surface 42 a of a blade 36 instead of the nominal surface 42 at the suction side of the blade 36 is used as a reference surface in order to position the blade onto the hub 34 in the LFW procedure, the finished suction side surface 42 a in the integrally bladed rotor 32 will be in a position relative to the hub 34 defined substantially in accordance with the nominal surface design data of the determined priority surface of the blade in the integrally bladed rotor, as presented in the CAD design drawing. In other words, the finished suction side surface 42 a will have a most accurate position, perhaps with an acceptable positioning tolerance in the integrally bladed rotor 32, thereby providing aerodynamic performance closest to the designed functionality.

Nevertheless, other finished surfaces such as a finished pressure side surface 44 a, finished leading edge surface 46 a or finished trailing edge surface 48 a follows the finished suction side surface 42 a in the positioning step of the LFW procedure. Therefore, the finished surfaces 44 a, 46 a and 48 a will not be as close to respective positions defined by the design data of their corresponding nominal surfaces 44, 46 and 48 as presented in the design drawing, as the finished suction side surface 42 a as the reference surface is to the nominal suction side surface 42, considering the fabrication tolerances between the respective finished surfaces and their corresponding nominal surfaces. Therefore, the aerodynamic performance of these finished surfaces of the blade may be somewhat affected during engine operation. Accordingly, the priority surface of the blade used as a reference surface in the positioning step of the LFW procedure, may be determined in accordance with the importance of surface functionality of the blade. In different engine designs, priority considerations may vary and therefore, for example, the finished pressure side surface 44 a, finished leading edge surface 46 a or finished trailing edge surface 48 a may be determined as a priority surface in different engine designs.

Referring to FIGS. 3 and 4, a set up system 50 according to one embodiment may be used in a LWF procedure to adjust a position of the respective blades 36 to a hub 34 a (which is schematically illustrated in a configuration similar to but not exactly the same as the hub 34 shown in FIG. 2). The set-up system 50 is capable of adjusting the position of each blade 36 in six dimensional degrees as indicated by the arrows relating to an X/Y/Z coordinate system. The set-up system 50 may be incorporated into a welding machine designed for an LFW procedure of an integrally bladed rotor 32, or may be implemented as an additional fixture apparatus which is used for positioning and holding each of the respective blades 36 and the hub 34 a in position during the LFW operation. When the hub 34 a and one of the blades 36 are both secured on the set-up system 50, the set-up system 50 allows the blade 36 to be moved along X axis which is perpendicular to joining surface 52 a of the hub 34 a, until joining surface 52 b of the blade 36 reaches the joining surface 52 a of the hub 34 a. The set-up system 50 also allows small offsets of the blade 36 in the direction of axes Y and Z which are parallel to the joining surface 52 a of the hub 34 a and allows a minor rotation about each of the axis X, Y, Z in order to position a finished surface such as the suction side surface 42 a of the blade 36 (which for example, has been determined as a priority surface of the blade in accordance with importance of blade functionality in this particular engine design) in the best position/orientation on the hub 34 a in accordance with the design data of the nominal suction side surface 42 presented in the design drawing of the integrally bladed rotor 32. Once the blade 36 is positioned on the hub 34 a in the best position/orientation, the set-up system 50 holds both the hub 34 a and the blade 36 in position and the LFW step is then conducted to weld the blade 36 to the hub 34 a. The above described steps may be repeated to position and then weld the respective remaining blades 36 on the hub 34 a.

The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departure from the scope of the described subject matter. For example, the described method is not limited to any particular integrally bladed rotor configuration such as that which is illustrated in the drawings, but may apply to many different types of rotor configurations. The described method is not limited to LFW welding operations but may apply to other joining procedures for attachment of the respective blades to a hub. Still other modifications which fall within the scope of the described subject matter will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims. 

The invention claimed is:
 1. A method of fabricating an integrally bladed rotor of a gas turbine engine, the integrally bladed rotor including a hub with an array of airfoil blades welded to the hub, the method comprising: a) determining a priority aerodynamic-functional surface of the respective blades in relation to importance of surface functionality of the blades during engine operation; b) positioning the respective blades onto the hub by using an entire finished surface of the determined priority aerodynamic-functional surface of the blades as a reference surface in order to locate a position of the respective blades on the hub; and c) welding the respectively positioned blades to the hub.
 2. The method as defined in claim 1 wherein step (b) is conducted by defining a position of the entire finished surface of the determined priority aerodynamic-functional surface of the respective blades substantially in accordance with nominal surface design data of the determined priority aerodynamic-functional surface of the respective blades in the integrally bladed rotor.
 3. The method as defined in claim 1 wherein an entire finished surface on a suction side of the respective blades is used as the reference surface.
 4. The method as defined in claim 1 wherein an entire finished surface on a pressure side of the respective blades is used as the reference surface.
 5. The method as defined in claim 1 wherein an entire finished surface on a leading edge of the respective blades is used as the reference surface.
 6. The method as defined in claim 1 wherein an entire finished surface on a trailing edge of the respective blades is used as the reference surface. 